Constraints on spin-dependent parton distributions at large x from global QCD analysis

We investigate the behavior of spin-dependent parton distribution functions (PDFs) at large parton momentum fractions x in the context of global QCD analysis. We explore the constraints from existing deep-inelastic scattering data, and from theoretical expectations for the leading x -> 1 behavior based on hard gluon exchange in perturbative QCD. Systematic uncertainties from the dependence of the PDFs on the choice of parametrization are studied by considering functional forms motivated by orbital angular momentum arguments. Finally, we quantify the reduction in the PDF uncertainties that may be expected from future high-x data from Jefferson Lab at 12 GeV.Comment: 14 pages, 3 figures, 1 tabl

Sagnac Effect of Goedel's Universe

We present exact expressions for the Sagnac effect of Goedel's Universe. For this purpose we first derive a formula for the Sagnac time delay along a circular path in the presence of an arbitrary stationary metric in cylindrical coordinates. We then apply this result to Goedel's metric for two different experimental situations: First, the light source and the detector are at rest relative to the matter generating the gravitational field. In this case we find an expression that is formally equivalent to the familiar nonrelativistic Sagnac time delay. Second, the light source and the detector are rotating relative to the matter. Here we show that for a special rotation rate of the detector the Sagnac time delay vanishes. Finally we propose a formulation of the Sagnac time delay in terms of invariant physical quantities. We show that this result is very close to the analogous formula of the Sagnac time delay of a rotating coordinate system in Minkowski spacetime.Comment: 26 pages, including 4 figures, corrected typos, changed reference

Quantum control on entangled bipartite qubits

Ising interaction between qubits could produce distortion in entangled pairs generated for engineering purposes (as in quantum computation) in presence of parasite magnetic fields, destroying or altering the expected behavior of process in which is projected to be used. Quantum control could be used to correct that situation in several ways. Sometimes the user should be make some measurement upon the system to decide which is the best control scheme; other posibility is try to reconstruct the system using similar procedures without perturbate it. In the complete pictures both schemes are present. We will work first with pure systems studying advantages of different procedures. After, we will extend these operations when time of distortion is uncertain, generating a mixed state, which needs to be corrected by suposing the most probably time of distortion.Comment: 10 pages, 5 figure

Global food demand and the contribution of livestock as we enter the new millennium

People in developed countries currently consume about 3 to 4 times as much meat and fish, and 5 to 6 times as much milk products per capita as in developing Asia and Africa. Meat, milk, and fish consumption per capita has barely grown in the developed countries as a whole over the past 20 years. Yet poor people everywhere clearly desire to eat more animal protein products as their incomes rise above poverty level and as they become urbanized. Growth in per capita consumption and production has in fact occurred in regions such as developing Asia, and most particularly China. Per capita consumption of animal proteins and use of cereals as feed in Asia have both grown in the 3 to 5 percent per annum range over the past 20 years. By 2020, according to IFPRI's IMPACT model projections, the share of developing countries in total world meat consumption will expand from 47 percent currently to 63 percent. IMPACT projections under various technical and economic assumptions suggest that there is enough production supply response in world systems to accomplish these production increases smoothly. Sensitivity analysis of the impact of restrictions on China's ability to produce more feedgrains illustrates that in a system of linked global markets for cereals and livestock products, such restrictions are not effective at lowering Chinese livestock consumption, which is driven by global trade in manufactures, although they do lower Chinese livestock production. The resulting imbalance raises world feed costs by one-third in 2020 over anticipated levels, encourages increased livestock exports from Latin America, discourages livestock exports from the U.S., and reduces meat and cereals imports and consumption in the poorer countries of Africa and Asia.Food consumption forecasting. ,Proteins in human nutrition. ,Livestock China. ,China ,

LIVESTOCK TO 2020: THE REVOLUTION CONTINUES

This paper was presented at the INTERNATIONAL TRADE IN LIVESTOCK PRODUCTS SYMPOSIUM in Auckland, New Zealand, January 18-19, 2001. The Symposium was sponsored by: the International Agricultural Trade Research Consortium, the Venture Trust, Massey University, New Zealand, and the Centre for Applied Economics and Policy Studies, Massey University. Dietary changes, especially in developing countries, are driving a massive increase in demand for livestock products. The objective of this symposium was to examine the consequences of this phenomenon, which some have even called a "revolution." How are dietary patterns changing, and can increased demands for livestock products be satisfied from domestic resources? If so, at what cost? What will be the flow-on impacts, for example, in terms of increased demands for feedgrains and the pressures for change within marketing systems? A supply-side response has been the continued development of large-scale, urban-based industrial livestock production systems that in many cases give rise to environmental concerns. If additional imports seem required, where will they originate and what about food security in the importing regions? How might market access conditions be re-negotiated to make increased imports achievable? Other important issues discussed involved food safety, animal health and welfare and the adoption of biotechnology, and their interactions with the negotiation of reforms to domestic and trade policies. Individual papers from this conference are available on AgEcon Search. If you would like to see the complete agenda and set of papers from this conference, please visit the IATRC symposium web page at: http://www1.umn.edu/iatrc.intro.htmDemand and Price Analysis, Production Economics,